1. Field of the Invention
This invention relates to a zoom lens, and particularly to a compact zoom lens suitable for use with a lens shutter camera.
2. Related Background Art
Zoom lenses are becoming mainstream in the field of photo-taking lenses for use with recent compact cameras of the lens shutter type. Particularly, various two-group zoom lenses comprising a simple construction have been proposed, and for example, Japanese Patent Application Laid-Open No. 2-73322 discloses a zoom lens of six-group six-lens construction, and Japanese Patent Application Laid-Open No. 4-225309 discloses a zoom lens of five-group six-lens construction. Also, Japanese Patent Application No. 3-319829 discloses an example in which an aspherical surface is introduced into a second lens group in order to achieve compactness and a high performance.
In the zoom lens disclosed in Japanese Patent Application Laid-Open No. 2-73322, a first lens group has comprised, in succession from the object side, a first positive lens component, a second negative lens component, a third positive lens component and a fourth positive lens component. However, since the second negative lens component and the third positive lens component are a biconcave lens and a biconvex lens, respectively, this zoom lens has suffered from the inconvenience that the deterioration of image when these lenses are decentered relative to each other is great.
In the zoom lens disclosed in Japanese Patent Application Laid-Open No. 4-225309, the second lens component and the third lens component are cemented together to thereby solve the above-mentioned problem. This zoom lens, however, has suffered from the inconvenience that the Abbe number of the second lens component is small and the correction of chromatic aberration is not sufficient.
Also, in achieving compactness, it is effective to make the refractive powers of the first lens group and second lens group great. However, the refractive power distribution with a stop interposed between the two lens groups becomes extremely asymmetrical and therefore, it becomes difficult to correct positive distortion at the wide-angle end and further, it is difficult to well correct the fluctuation of off-axis aberration caused by the angle of field, and this has led to the inconvenience that it is difficult to achieve compactness.
In order to solve this inconvenience in the zoom lens disclosed in Japanese Patent Application No. 3-319829, an aspherical surface has been introduced into the second lens group, but the position of the principal point of the first lens group lies -toward the image plane, and this is not very suitable for compactness and has led to the inconvenience that a zoom ratio of about 1.7 times is the limit.
The present invention has been made in view of the above-noted problems and the object thereof is to provide a compact zoom lens of high performance comprising a simple construction of a zoom ratio of about 2 times.